1. Field of the Invention
This invention relates to a method for reducing the presence of human enteropathogenic bacteria in poultry.
2. Description of the Prior Art
The consumption of improperly prepared poultry products has resulted in numerous cases of human intestinal diseases. It has long been recognized that Salmonella spp. are causative agents of such diseases, and more recently Campylobacter spp., especially Campylobacter jejuni, has also been implicated. As many as two million cases of salmonellosis occur annually in the United States (Stavric et al., Journal of Food Protection, Volume 56, No. 2, 173-180, February 1993); twice as many cases of campylobacteriosis are thought to occur (Krienberg et al., Food Technology, pages 77, 80, 81, and 98, July 1987). Both microorganisms may colonize poultry gastrointestinal tracts without any deleterious effects on the birds and, although some colonized birds can be detected, asymptomatic carriers can freely spread the microorganisms during production and processing, resulting in further contamination of both live birds and carcasses. Poultry serves as the primary reservoir for Salmonella and Campylobacter in the food supply (Jones et al., Journal of Food Protection, Volume 54, No. 4, 259-262, April 1991; Jones et al., Journal of Food Protection, Volume 54, No. 7, 502-507, July 1991). The intestinal contents of chickens may harbor up to 10.sup.7 Campylobacter and/or Salmonella per gram, and cross contamination during processing is frequent (Oosterom et al., Journal of Food Protection, Volume 46, No. 4, 339-344, April 1983). Studies have demonstrated that fecal material constitutes the major source from which edible parts of chickens are contaminated in processing plants. Therefore, to significantly reduce the level of contamination on processed poultry, pathogen-free or nearly pathogen-free birds must be delivered to the processing plant, (Bailey, Poultry Science, Volume 72, 1169-1173, 1993).
Better control measures are needed to minimize the spread of these and other human enteropathogenic bacteria; and the most promising approach to achieve this end has been to decrease the incidence and level of colonization by these microorganisms in poultry gastrointestinal tracts. To date, the most effective means for controlling Salmonella colonization is competitive exclusion (CE). Although the exact mechanism of CE protection is unclear, it is likely to be influenced by factors such as pH, Eh, production of inhibitory substances such as H.sub.2 S, bacteriocins, fatty acids, and conjugated bile acids; competition for nutrients and receptor sites; and local immunity (Mead et al., Letters in Applied Microbiology, Volume 10, 221-227, 1990). Competitive exclusion treatment involves introduction of intestinal flora from pathogen-free adult birds into newly hatched chicks. A study by Nurmi et al. (Nature, Volume 241, 210-211, Jan. 19, 1973), first reported the use of the competitive exclusion technique. The reference discloses inoculation of 1 to 2 day old chicks by oral gavage with a 1:10 dilution of normal intestinal contents from healthy adult birds. One day later, the chicks were challenged with Salmonella. After 8-22 days, the birds were examined for the presence of Salmonella. It was found that only 33% of the treated birds were colonized with Salmonella whereas 100% of the untreated birds were colonized with Salmonella. Originally, a suspension of crop and intestinal tract materials obtained from healthy, adult birds was used. In later studies, cecal content was cultured anaerobically in a liquid medium. It was found that preparations of subcultured intestinal contents from healthy, adult birds conferred protection to young chicks whose intestinal or gut microflora had not yet been established. Administration of undefined CE preparations to chicks speeds up the maturation of the gut flora in the newly-hatched birds and also provides a substitute for the natural process of transmission of microflora from the adult hen to its offspring. Snoeyenbos et al., U.S. Pat. No. 4,335,107 (1982) developed a technique designed to reduce salmonellae in poultry where the source of CE microflora was lyophilized fecal droppings which were propagated by anaerobic culture. Mikkola et al., U.S. Pat. No. 4,657,762 (1987) discloses the use of intestinal fecal and cecal contents as a source of CE microflora. Treatment with their culture required media to be anaerobic and pH balanced. Neither of these CE treatments addressed Campylobacter.
Since CE was known to be effective against Salmonella, a similar method for the control of Campylobacter was investigated by Stern et al. (Avian Diseases, Volume 32, 330-334, 1988). It was found, however, that treatment with CE preparations such as described by Nurmi et al. (1973), Snoeyenbos et al. (1982) and Mikkola et al (1987), did not affect Campylobacter colonization. After treatment with five different CE cultures, colonization was observed after challenge by Campylobacter in 81 of 84 chicks, and 45 of 46 control chicks. Shanker et al. confirmed these observations (Epidemiol. Infect., Volume 104 101-110, 1990). Stern and Stern et al. (Poultry Science, Vol. 73, 402-407, 1994; and U.S. patent application Ser. No. 08/031,983, which are both herein incorporated by reference) disclose a mucosal competitive exclusion (MCE) method and preparation effective against Campylobacter and Salmonella, using an anaerobic culture of the mucin layer scraped from cecal epithelia and an anaerobic culture of a cut piece of the washed ceca. This undefined MCE culture contains a diversity of flora that successfully competes with Salmonella and diminishes levels of Campylobacter in the chick.
The treatments discussed above all relate to the use of undefined mixtures of organisms obtained from cecal contents or cecal wall scrapings which are subcultured. While these undefined cultures have generally proven to be effective in reducing colonization of chickens with foodborne pathogens, there are concerns regarding their safety since there is the possibility of transmission of etiological agents associated with human foodborne disease and/or the transmission of avian disease.
Because of the safety concerns and difficulties in standardizing the bacterial composition and/or efficacy of undefined CE cultures, there is a need to develop defined compositions which exhibit the potency of undefined culture in order to diminish the presence of human enteropathogenic bacteria in poultry. Stavric et al. (Journal of Food Protection, Volume 56, No. 2, 173-180, February 1993) disclose that the formulation of effective defined cultures is difficult because of insufficient knowledge of the underlying protective mechanism(s) and interactions between gut microflora. Furthermore, the reference discloses, there is a lack of a sound scientific basis for the selection of potentially protective strains. To date, defined cultures of single isolates of Clostridium spp., Streptococcus faecalis, Bifidobacterium spp., and Bacteroides hypermegas have been examined. Furthermore, preparations containing several strains of single species, such as Bacteroides spp., Bifidobacterium spp., and Escherichia spp. have also been evaluated. None of these CE preparations consistently protect chicks against Salmonella challenge. The reference states that there has been one report claiming mixtures of lactobacilli protect poultry against Salmonella colonization.
Stavric further reports that the use of probiotics containing one to eight bacterial strains of different genera failed to protect poultry against Salmonella, although the data is limited. Studies with larger numbers of bacterial strains from different genera have shown limited success. Therefore, it was surprising to find that the present invention, which is a defined CE preparation of yeast, reduced the populations of Gram-negative enteropathogenic Campylobacter and Salmonella in poultry.